Method of coating strip steel and products thereof



-May 3, 1938. M. RUBIN ET AL. 2,115,750

METHOD OF COATING STRIP STEEL AND PRODUCTS THEREOF Filed July 15 1936 VINVENTORJ 7%?0/146/ fuzrr M Zia 7,6/1 d/ezazzdar fi ATTORNEYS PatentedMay 3, 1938 I V UNITED STATES PATENT orrlcs METnon or ooATING STRIPSTEEL AND raonuczrs TnEaEor Michael Rubin and Ralph E. Alexander,Warren, Ohio, assignors to The Thomas Steel Company, Warren, Ohio, a.corporation of Ohio Application July 13, 1936, Serial No. 90,298

4 Claims. (Cl. 20414) This invention relates, as indicated, to a methodof coating strip steel, but has reference more particularly to acontinuous method of coating strip steel with nickel, whereby a ductile,non- 5 porous, uniform and intimately bonded coating of nickel is formedon the steel.

The coating of tin on commercial tin plate, as now manufactured, is moreor less porous, so that containers for food stuffs or food products madefrom such tin plate are not entirely resistant to the attack of chemicalcompounds contained in preserved food stuffs, fruit juices, etc.Moreover, the tin coating does not adhere tenaciously to the base metal,is rather soft and easily abraded, and is therefore likely to becomepunctured or ruptured during handling of the tin plate or during thecontainer-forming operation.

The invention accordingly has as its primary object the provision ofsteel strip having a coating of an impervious, non-porous nature, whichcoating forms a protective medium for the strip, enabling the strip toresist corrosion and rendering it especially suitable therefore, formanufacture into containers for food stuffs and food products.

Another object of the invention is the provision of steel strip of thecharacter described in which the coating is much harder than the coatingof tin plate and adheres with a high degree ofv tenacity to the basemetal, thereby facilitating handling of the strip and formation thereofinto containers, without danger of puncturing or rupturing the coatingduring the handling and container-forming operations.

A further object of the invention is to provide a method of coating suchstrip which is of a continuous character, whereby production of thecoated strip in desired commercial quantities is made feasible.

To the accomplishment of the foregoing and related ends, said invention,then, consists of the steps hereinafter described and particularlypointed out in the claims; the annexed drawing and the followingdescription setting forth in 45 detail one approved method of carryingout the invention, such disclosed steps illustrating, however, but oneof the various ways in which the principle of the invention may be used.

The method, broadly stated, consists in bringing the steel strip and thenickel into intimate contact, and while in such relation subjecting thesame to heat under such conditions and for such a length of time as .toeifect a desired diflusion of the metals" and a desired condition in thenickel constituent. In carrying out the heating step,

the same may be governed or controlled in such a manner, particularly asregards the temperature and time period, as to effect an annealing ofthe base metal and at the same time obtain the desired diffusion andcondition of the nickel coat- -A simple and emcient means'of bringingthe metals into intimate contact is by electro-deposition of the nickelon the surface of the ferrous strip, the deposit being 01 anydesiredthickness and the deposition being accomplished by any of theapproved methods of nickel plating. An electro-deposited coating ofnickel is, however, of a porous nature and is capable of being strippedfrom the steel strip. Electro-deposited nickel accordingly does notprovide an efficient corrosion-resisting covering as corrosion of thesteel strip may start in the pin holes resulting from the porous natureof the nickel. However, the steel strip with its electro-depositedcoating is subjected to a heating,or what may be termed as an annealingstep in the process, in order to strongly unite the metals and renderthe electrodeposited nickel substantially impervious and ductile. Thisannealing step is preferably carried out in a furnace in which a neutralor reducing. atmosphere is maintained as by means of gases, such ashydrogen and carbon monoxide, whereby oxidation of the metals isprecluded during the heating and cooling periods.

The heating or annealing is accomplished at temperatures ranging fromabout 1100 F, to about 1800" F., the metals diffusing into one anotherto form a solid solution zone at their contiguous surfaces, and in thismanner the iron and nickel constituents are tenaciously united. Theheating is at all times controlled with respect to duration as to securea definite depth'of diffusion of the nickel into the ferrous metal, butrestricting the solid solution zone to a .depth less than that of thethickness of the nickel body constituting the coating. If the depth ofthe solid solution zone does not exceed the above indi-' catedthickness, the exposed surface will be substantially pure nickel andfree from pin holes.

The heating moreover liberates and drives off any occluded gases, suchas hydrogen, which may be taken up during electro-deposition, therebymaking the coating more ductile and impervious.

The method may be practiced commercially by means of the apparatus shownin the accompanying drawing. 1

Referring to said drawing, the strip S is drawn from a, coil mounted onreel I, and is passed successively through an alkali cleaning tank 2, arinse tank 3, an acid pickling tank 4, another rinse tank 5, a nickelplating tank 6, a rinse tank I, a drying oven 8, a. furnace 9 comprisingan annealing chamber In and a cooling chamber H, and is coiled up on atake-up reel l2.

Satisfactory results have been obtained by first electro-depositingone-tenth of an ounce of nickel per square foot of surface upon theferrous strip in the plating bath 6 and by heating the strip thus coatedin the chamber ill at a temperature of about 1650 F., the strip passingthrough the furnace at a speed of about 14 feet per minute. The strip,upon emerging from the heating chamber I is cooled in the coolingchamber l at such a rate as will produce the desired annealing of thesteel strip. A reducing atmosphere is at all times maintained within thefurnace 9. The method is thus carried out in a continuous manner and ata uniform speed.

We have found that when the nickel coating has been applied and treatedin'this manner that it becomes strongly bonded to the steel strip and isof an impervious, lustrous and ductile nature. The thickness of thenickel coating may be varied as desired. By using a lower temperaturefor the annealing and increasing the duration of such annealing, resultscomparable to those obtained by using higher temperatures and shorterperiods of annealing may be secured, as will be readily understood. Anydesired surface appearance, from a matte to a bright mirror finish, maybe obtained by proper polishing and/or buffing procedures.

Other modes of applying the principle of our invention may be employed.instead of the one explained, change being made as regards the methodherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

We therefore particularly point out and distinctly claim as ourinvention:

1. The method of coating steel strip and the like which comprisesconsecutively subjecting the strip to the action of a nickel platingbath to form a coating of nickel thereon and to heating at a temperatureof from about 1100 F. to about 1800 F. in a non-oxidizing atmosphere,whereby to form a solid solution zone at the contiguous surfaces of thesteel strip and nickel.

2. The method of coating steel strip and the like which comprisescontinuously moving and consecutively subjecting the strip to the actionof a nickel plating bath to form a coating of nickel thereon and toheating at a temperature of from about 1100 F. to about 1650 F. in anon-oxidizing atmosphere, whereby to form a solid solution zone at thecontiguous surfaces of the steel strip and nickel.

3. The method of coating steel strip and the like which compriseselectro-depositing nickel upon the strip, then passing the strip througha furnace chamber in which .a reducing atmosphere is maintained andwherein the strip is heated to a temperature of from about 1100 F. toabout 1650 F. whereby a solid solution zone if formed at the contiguoussurfaces of the steel strip and nickel, and then cooling the strip atsuch a rate as will produce the desired annealing of the strip.

4. The method which comprises cleaning steel strip, depositing a coatingof nickel thereon, then passing the strip through a furnace chamber inwhich a reducing atmosphere is maintained and wherein the strip isheated to a temperature of from about 1100 F. to about 1650 F., and thencooling the strip at a controlled rate.

MICHAEL RUBIN. RALPH E. ALEXANDER.

